Second generation FLIR common modules

ABSTRACT

An improved modular FLIR system is provided that fits in the same space  elopes that were provided for the Army&#39;s GEN I FLIR&#39;s. The resolution is more than doubled by using a narrow two dimensional array of Hg-Cd-Te detectors with pn junctions as a time-delay-integration line sensor, improved optics and analog-digital conversion with image enhancement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to Forward Looking Infrared(FLIR) Imaging Systems as used by the U.S. Army and other military orcivilian organizations.

2. Description of Prior Art

The Army has adopted a first generation (GEN I) common module approachfor the production and fielding of Forward Looking Infra-Red sensors(FLIR's). This concept provides common access to core FLIR components inorder to reduce costs and facilitate maintenance, but yet still allowssystem integrators the flexibility of configuring each particular sensorto individual needs. There are several shortcomings to the common moduleconcept, however. Due to the variety of sensor requirements andtechnology improvements, each common "module" evolved into a family ofmodules and thus complicated supply and repair logistics. Expensivemodule interfaces have been developed for each sensor platform.Centralized universal upgrades have not been possible. The performanceof each sensor is often very different from any other, thus complicatingtraining and strategic deployment. Many improvements in the technologyof infra-red sensoring and imaging have since been made to the extentthat it is neither cost effective nor physically possible to modify GENI Common Module FLIR sensors to achieve enhanced performance. Rather thestate of the art is now such that a new generation of FLIR sensors mustbe established. Examples of these technology advancements include theavailability of multi-element photovoltaic (PV) focal plane arrays,time-delayed-integration (TDI) for enhanced sensitivity, miniaturizedelectronic multiplexer circuitry, digital video image processing,improved cryogenic cooling, long lifetime unidirectional scanners andintegrated laser-hardened optics. Advances have also been made in thecreation of two dimensional staring arrays which do not requirefield-of-view scanning, but the general consensus is that thistechnology is too immature to match the performance of the proposed newGEN II scanning FLIR sensor system, to be described. It has beendetermined that the Army would greatly benefit from the development of anew Kit concept, wherein GEN II FLIR technology is fielded in the formof preassembled kits ready to install into at least three generalcategories of Army FLIR environments, large Attack Helicopters, Tanks orArmored Vehicles, and smaller Scout class vehicles.

SUMMARY OF THE INVENTION

According to the invention, all of the Army's current FLIR sensor needscan be met by supplying three new FLIR kits. These kits will providebetter resolution, countermeasure resistance, video processing, and datatransfer than the first generation FLIR's and will support eitherdigital or analog processors. The first Kit, designated as Night Vision(NV)-80, will serve all major ground vehicle systems such as tanks,missile launchers, augmenting viewers, sights and intelligence gatheringequipment. The second kit, designated as NV-81, is designed for turretedhelicopter aircraft like the Apache and Comanche requiring wide,pilotage application fields of view. A third kit, designated NV-82, isdesigned for aircraft with turrets having wide apertures or three-wayfields of view, also common to Apache and Comanche aircraft that useFLIR sensors for targeting applications. Certain modules within thesekits that will be designed to be mixed and matched, thus permitting themto serve a wide range of requirements that may arise in the future.

One object of the invention is to provide FLIR kits having reliable andenhanced performance complying with efficient new predefined envelopesand interfaces for the Army's and other services' second generation ofNight Vision equipment.

A further object of the invention is to provide a minimum of kits formedfrom a minimum number of components or modules to meet all the currentneeds of the Army.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

FIG. 1 is a pictorial view of a prior art GEN I Forward Looking Infrared(FLIR) imaging system based only on standard modules;

FIG. 2 is a front view of a detector line array as used in above GEN Isystem;

FIG. 3 is a pictorial view of a GEN II system that will replace thesystem in FIG. 1; and

FIG. 4 is an exploded view of a two dimensional detector array as usedin above GEN II system showing the kit within a dashed outline.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

As illustrated in FIG. 1, the U.S. Army currently uses First Generation(GEN I) FLIR common modules in nearly all major sensor platforms today.A platform is a support placed on a weapon system, a surveillancesystem, a vehicle or any combination of these systems to which FLIRsensor modules may be conveniently attached. The Afocal Assembly 10 isconsidered to be part of the platform, for example this assembly may befixed mounted unit initially provided for a daylight sight or guncamera. Outfitting the assembly with IR lenses in the 8 to 12 micronrange, hereafter referred to as far-infrared readies it for FLIR use.

The scanner module 11 contains an oscillating mirror 11A that providesoperates at 30, 45, or 60 cps. The IR radiation after being reflectedabout 90° by the scanner mirror is passed to an IR imager module 12,which focuses the scanned image of the scene, gathered by the afocal,through an IR window onto a small array chip or sensor mounted in adewar module 13. The sensor or detector is a linear array of discretelight sensitive electronic elements, oriented normal to the optical axisand the direction of scan, e.g. vertical to a horizontal scan. As thescanner pans this array across the horizontal field of view, theelectronics read out an entire two dimensional FOV within the time frameof one scan. A slight relative rotation or nodding motion of the scannerbetween scans is used to provide mechanical interlace. Interlace linesare produced by each successive scan. The scanner can snap back to itsinitial position (Uni-Directional) after a complete scan or generate areverse scan (Bi-Directional) to return to that position. To provide auseable S/N value, the chip is cooled by a cryogenic dewar module 14with a cold finger 14A that extends through the dewar to gently touchthe chip and extract heat from it.

As shown in FIG. 2, the detector chip 13B carries a line array offar-infrared detectors 13C that produce 160, 320 or 480 resolution linesgenerated in parallel. Each detector output is interfaced with an inputon a different preamplifier 15A and post amplifier 15B in an electronicsmodule, usually through a harness 13A. Integrated circuits in thismodule provide the preamps, postamps and sometimes simple logic circuitsto compensate for image distortion. Dotted line 13D denotes the motionof an IR image pixel on the forward scan of the imager and dotted line13E indicates the motion of the same pixel during the return scan.

Referring again to FIG. 1, the electronics module has an output for eachline post-amplifier 15B to interface a Light Emitting Diode (LED) module16. An LED is provided for the postamplifier of each detector in theDewar Module. The LED's thus mirror the responses of the photodiodes asa visible light line image. Reflecting the light from the LED's about90° using the back of the vibrating mirror 11A recreates thefield-of-view (FOV) of the image from the Afocal Assembly in visiblelight. A Binocular Eyepiece Module 18 is commonly placed in the path ofthe recreated image reflecting it to a convenient viewing angle andimaging the scene for a human eyes. The electronics module may alsoinclude integrated circuits with a single output to delay and reformatthe detector signals into a video signal like that used in standardtelevision.

Such modules, or common modules in the first generation, are part of afamily that includes the standardized modules in the Module Table below.Each user purchases the standardized or specialized modules required forhis mission; combines them and installs the necessary platform tointerface his system, e.g. a man portable system, a land vehicle, amarine vessel, or an aircraft. A few man-portable systems have escapedthe modular concept in order to reduce their weight, since they areinherently simple low resolution systems. Vehicle systems, on the otherhand, tend to become more complex high resolution systems that benefitfrom the modular approach. Numerous improvements have been made in thetechnologies that govern the make up of the modules, some of which havebeen compromised to meet current module criteria and others have beenshelved until these module constraints are removed. Similarly,technological advancements and improved system performance requirementsdemand a more integrated approach to interfacing these new modules. Thishas reached a state that warrants a new second generation of kitscomposed of new modules.

    ______________________________________    Module Table for GEN-1 FLIR    DESCRIPTION             NUMBER    ______________________________________    Preamplifier Video      AM-6923/UA    Postamplifier - Control Driver                            AM-6924/UA    Regulator, Voltage, Bias (Large 5 volt)                            CN-1503/UA    Regulator, Voltage, Bias (Small 3 volt)                            CN-1559/UA    Auxiliary Control, Video                            PL-1402/UA    Scan-Interlace (Small, 30 Hz)                            PL-1403/UA    Scan-Interlace (Small, 30 Hz)                            PL-1403A/UA    Scan-Interlace (Large, 40-60 Hz)                            PL-1408/UA    Detector - Dewar (Small, 60 element)                            DT-591A/UA    Detector - Dewar (Large, 120 element)                            DT-617A/UA    Detector - Dewar (Large, 180 element)                            DT-594/UA    Detector - Dewar (Large, 180 element)                            DT-594A/UA    Cooler, Cryogenic Mechanical (1W Low Vib)                            HD-1033B/UA    Cooler, Cryogenic Mechanical (1w Low Vib)                            HD-1033C/UA    Cooler, Cryogenic Mechanical (Split .25w)                            HD-1045(V)/UA    Cooler, Cryogenic Mechanical (Split 1W)                            HD-1111(V)/UA    Cooler, Cryogenic Mechanical (Integ. .25)                            HD-1132(V)/UA    Cooler, Cryogenic Mechanical (Integ. 1W)                            Not Assigned    Scanner,Mechanical      MX-9872(V)1/UA    Scanner,Mechanical      MX-9872(V)2/UA    Scanner,Mechanical      MX-9872(V)3/UA    Scanner,Mechanical      MX-9872(V)4/UA    Scanner,Mechanical      MX-9872(V)5/UA    Scanner,Mechanical      MX-9872(V)6/UA    Light Emitting Diode Array (180 element)                            SU-96/UA    Light Emitting Diode Array (120 element)                            SU-122/UA    Light Emitting Diode Array (90 element)                            SU-127/UA    Imager, Optical (Small) SU-97/UA    Imager, Optical (Small) SU-97B/UA    Imager, Optical (Large) SU-103/UA    Imager, Optical (Large) SU-103A/UA    Imager, Optical (Large) SU-121/UA    Collimator, Visual (Small)                            SU-98/UA    Collimator, Visual (Large)                            SU-102/UA    ______________________________________

Referring now to FIG. 3, there is shown, in a pictorial block diagram,the components of a GEN II IR imaging kit. At present, only componentswithin the dashed outline are to be parts of this kit, futurerequirements may require that ATR's and digital enhancement modules beincluded as well. The first component or module 30 has a first housing30A that contains the afocal lens system. This system includes anobjective lens 30B to gather light from a distant scene and/or targetobject. The scene is first lo focused on an intermediate focal planewithin the module that contains a number of thermal references 30C. Thelight from the scene image and references is gathered by a collimatinglens 30D and emerges as parallel rays focussed at infinity. The lensesrequire special materials and treatment to reduce absorption of thefar-infrared, which not only reduces available flux but also heats upmodular components causing malfunctions. The focal plane referencesrequire a regulated d.c. input and a control feedback loop to theimaging system to perform their function furnished by one or more leadslike lead 30E. This focal plane is also an excellent plane in which toplace a filter 30K to prevent overloading the detectors or providebetter discrimination of certain targets. Rotating filter wheels withmany filters are often used to analyze atmospheric contaminants andthese may inserted in the focal plane and coupled to a SystemElectronics Component, to be described, by signal leads like 30E. Thelenses may include a motorized focussing mechanism 30F and thus requirea similar d.c. input lead 30G with reversible polarity for remotefocussing. The mechanical coupling or interface between the first andsecond modules thus requires a circular stop opening for the collimatedoutput image beam and half of a first electrical connector 30H with twopairs of mating contacts, like contact 30I insulated from the modulehousings which are commonly grounded. The interfaces between all modulesmay be the usual bolted flange type, like 30J with gaskets to seal outgrit particles and caustic atmospheric agents. The lenses or a thinplanar window may be provided as seals for the optical openings in themodule housings when separated. Electrical connectors are sealed throughby their insulation or suitable grommets.

The second component or module 31 is enclosed in a second housing 31Athe wall of which either contains the mating portion of said firstconnector or has leads sealed through the wall to it. Similar connectorswill be noted between successive modules as this description proceeds.The housing 31A encloses a mirror type scanner 31B driven by asynchronous motor 31C. Unlike the scanner in first generation modules,this scanner scans in one direction only (i.e. unidirectional mode). Therate of scanning is chosen to be 30, 45 or 60 cycles per second to matchelectronics modules to be described presently. The mirror may thus beone of n facets of a quiet and smooth running synchronized rotorspinning at 30/n 45/N or 60/n cycles per second. The mirror can alsoscan slowly and snap to its initial position to produce each scan, ifdesired. To maintain mirror motor synchronicity this module requires atleast a single phase motor input lead 31D carrying current with afrequency related to 15 cps, and might obviously benefit from two orthree such phase input leads. The interface between the second and thirdmodules must then include a stop aperture at least the height and twicethe width of that between the first and second modules. It also mustprovide half of a connector 31E with the same number of insulatedterminal pairs like pair 31F for dc and at least one terminal pair perphase of the motor input.

The third component or module 32 has a third housing 32A that containsan imaging lens system. A decollimating lens 32B focusses the collimatedbeam into an image of the scene plus references at a second focal plane,which like the first provides a good location for special filters, ifdesired. An ocular lens 32C matches the image size to an array 32D ofphotodiodes. These photodiodes are by nature photovoltaic devices whichare defined in Webster's Ninth New Collegiate Dictionary, Copyright1985, as being "of, relating to or utilizing the generation of a voltagewhen radiant energy falls on the boundary between dissimilar substances(as two different semiconductors)". It is well known that HgCdTephotodiodes are photovoltaic devices and this is evidenced by theterminology used in U.S. Pat. No. 4,318,217 entitled "METHOD OFMANUFACTURING AN INFRA-RED DETECTOR DEVICE" granted to Michael D.Jenner, et al. 9 Mar. 1982.

As shown in FIG. 4, the diodes 41 are square and arranged on a Hg-Cd-Techip 42 in vertical rows normal to the direction of image motion, e.g.horizontal motion, with vertical spaces between diodes equal somefraction of the diodes' height. The diodes in subsequent rows in thedirection of image motion are displaced a fraction of the width of adiode forming a set of four or more different rows. This pattern isrepeated n times to secure an increase in the signal to noise ratio ofn⁻². Chip 42 is mounted on a silicon based chip 43 carrying acharge-coupled-circuit (CCD) by means of solder bead connectors 44having the same pattern as the photodiodes, i.e. one for each diode.When heated and pressed together the silicon chip receives thephotodiode outputs from the Hg-Cd-Te chip and, when driven by a clocksignal at the scan frequency of the second module, samples thephotodiodes and formats their outputs into parallel and/or series typeanalog video type line output signals. Parallel readouts will of courseinvolve increased output leads, e.g. one lead per line of the image.This array will generate 480 lines per scan or a 960 line interlacedframe.

Returning to FIG. 3, a special dewar 32E is required for this array, asuitable embodiment of which is described in patent application Ser. No.08/176,866. The dewar must have an easily removable IR window to provideaccess to the detector array without removing the cold finger mountingto which it is attached. The dewar is a thin glass structure easilydamaged by the metal cold finger. This module must have a thermallyinsulated tubular fitting 32F that mounts through the module wall andthe wall of the dewar. The exterior end of the fitting couples to asection of cryogenic tubing 32G and this in turn couples to a cryogeniccooler 32H attached to the base of the module housing. Coolingrequirements vary with the size and sophistication of the chip. Balancedsplit cycle coolers from 0.25 to 1.75 watts, using helium as a coolant,are readily available in the art. A portion of the wall of this moduleis apertured to receive the remaining half of the second connector andhalf of a third electrical connector 32I. The third connector carriesterminal pairs, like pair 32J, wired to matching terminal pairs of thesecond connector. In addition it carries a terminal pairs for a dcvoltage lead 32K, a clock voltage input lead 32L and a video output lead32M for the line outputs from the silicon chip. The cooler has its ownconnector with terminal pair 32N for a power lead 320.

The fourth component or module 33 has a fourth housing 33A that containsthe electronic controls that feed the detector and reformat its output.The wall of this module is apertured for a standard input connector 33Bsupplying primary power such as n-phase 110 v 60 cps or other commonpower sources. This power is transformed into low voltage regulated acand dc outputs and clock pulse outputs. The above module wall is alsoapertured to receive half of the third connector. Appropriate ones ofthe above ac outputs are coupled to the third connector to power thefocussing and scan motors. A dc and clock signal in is suppliedintegrated circuits like the photodiode array and charge-coupled-device(CCD) that samples the photodiodes. They are also coupled to fourthmodule components such as preamps and postamps for the CCD outputs,image enhancing circuits, analog video formatting circuits, and analogto digital converters and digital storage (control and status) devices.The above module wall is also apertured to receive half of a powerconnector 33H for the cooler, and half of a fourth connector 33C for anoptional fifth module and a connector 33H for a TV type monitor ofeither analog or digital design. The fourth connector has terminal pairslike 33D for an ac Power lead 33E, a input interrogation signal lead 33Fto access information in the digital storage devices and an output lead33G to carry the information accessed to an optical device for furtherprocessing and/or use. The wall is further apertured to receive amonitor connector 33H having terminal pairs like 33I. One pair iscoupled to an ac power lead 33J for the monitor and another pair iscoupled to a video lead 33K which carries the accessed information froma display formatter to the monitor.

The above mentioned optional device, not now a part of the kit, may bean Augmented Target Recognition (ATR) device. Its wall would thus beapertured to receive the remaining half of the fourth connector. The ATRdevice includes Read-only-memories (ROM's) containing far infraredtarget signatures which form data banks on far-infrared target images.The ATR also has circuits known as segmenters wired to its half of thefourth connector in order to select specific portions of the digitaldata generated by the electronics in the fourth module. This device alsoincludes comparators which compare these specific portions with thetarget signatures stored in the data banks to generate recognitionprobabilities, classification possibilities, risk factor presented bythe target imaged by the FLIR and, if possible, proper responses,Numerous types of ATR's have been proposed, and many are designed tointerface other systems such as radar and sonar. The purpose here is toprovide a standard interface to such digital devices and analog deviceslike the TV type monitor. The latter requires a connector 34B with onlyone pair of terminals for a video lead to superimpose target symbols onthe scene generated by the fourth module.

The three Field Kits to be provided will be designated as the NV-80,NV-81 and NV-82. The NV-80 is a specific second generation FLIR kit foruse in land vehicles such as tanks, missile launchers and the like; theNV-81 is a second generation FLIR kit for pilot application use inaircraft; and the NV-82 is a complex second generation FLIR kit for usein aircraft with long range targeting sensors. The modules in each kitmay vary slightly, but commonality is preserved when possible. The 80model kit uses a detector with a one watt cooler, a non-interlace secondmodule and optical modules that provide narrow (2 degree×3.6 degree) andmedium (7.5×13.3) fields of view (FOV). All models use the same fourthmodule. The 81 kit uses an interlace scanner which captures 960 linesper frame twice that of the other kits. This kit uses optics for a verywide FOV (30×53.3). The 82 kit uses a detector designed for a 1.75 wattcooler. The resulting image is very free of noise and suitable for usewith ATR's. The first module of this kit is designed to give anintermediate FOV (6×10.6) because it is intended to interface withanother platform specific afocal assembly with multiple fields of view.

Having thus described my invention, what we claim as new and desire to secure by Letters Patent is as follows:
 1. A second generation Forward Looking Infrared (FLIR) kit comprisinga series of four modules, said modules having housings proportioned to fit within one of three geometric envelopes defined by spaces in Army vehicles that have been allotted to GEN I FLIR systems, the first two of said modules each having an optical axis with at least one variable far-infrared optical element along said axis, an optical input at one end of said axis for far-infrared radiation, at least one electrical input transducer coupled to each of said variable optical elements and external electrical inputs for dc and ac signals to energize the electrical transducers therein; the first and second of said modules having an optical output for said far-infrared radiation at the end of said axis opposite said one end; the third of said modules including an optical axis, an optical input at one end of that axis for far-infrared radiation, and external electrical inputs for dc and ac signals, said third module further including a dewar containing an array of mercury-cadmium-telluride far-infrared detectors with pn junctions, an input for cooling fluid circulated in said dewar and an electronic signal output connected to said detectors; the fourth of said modules having inputs and outputs for electronic signals only; and the respective pairs of said inputs and outputs being serially interconnected.
 2. A kit according to claim 1 wherein the first of said modules includes:an afocal lens comprising said at least one variable optical element and a collimating lens between said optical input and output, said afocal lens having a focal plane wherein the image of a distant scene is focused, thermal references mounted in said focal plane along the periphery of said focused image, whereby said collimating lens simultaneously gathers, combines and collimates infrared radiation from said distant scene and said references into a narrowed beam at said optical output.
 3. A kit according to claim 2 wherein the second of said modules includes:a scanning means comprising said at least one variable optical element between said optical input and output thereof to gradually displace said narrowed beam in only one scan direction normal to the optical axis of said beam for a distance about equal to the dimension of said narrowed beam in said scan direction and to restore said narrowed beam to its original position at the end of each scan.
 4. A kit according to claim 3, wherein:said scanning means redirects the optical axis of said displaced narrow beam at a right angle.
 5. A kit according to claim 3 wherein said third module includes:an ocular lens means substantially centered in said beam to focus a moving image of said scene and references on a focal plane in said third module; said array of detectors comprising a two dimensional image line sensing array of uniformly spaced far-infrared photodiodes mounted in said focal plane to form parallel rows, with n photodiodes in each row, n being orders of magnitude less than the number of rows, the rows being staggered and normally aligned with the direction of the image's motion to provide oversampled analog video response signals for time delay and integration; and a silicon based ccd integrated circuit means coupled with said array to produce photodiode output sampled signals in response to timed input clock signals, and to create analog video signals by delaying, shifting and integrating selected ones of said sampled signals.
 6. A kit according to claim 5 wherein said fourth module includes:a video output terminal for a monitor with a video input; and an analog signal processor means coupled between the output of said third module and said video terminal to format video input signals for said monitor.
 7. A kit according to claim 5 wherein said fourth module includes:an analog-to-digital converter means with an input coupled to the output of said third module to convert said analog video signals to digital video signals; and digital RAM storage means coupled to the output of said converter to store said digital signals.
 8. A kit according to claim 7 wherein said fourth module includes:digital processors coupled between the output of said converter and the input of said storage means to enhance the image quality of said digital video signals.
 9. A kit according to claim 5 wherein:said dewar surrounds said detectors and has an input tube to supply coolant, said dewar having a removable far-infrared window at one end covering said detectors, whereby said detectors can be removed without disassembling the detectors mounting structure from said dewar.
 10. A kit according to claim 9 wherein said third module further includes:an electrically powered cooling means, using a low density gas coolant, to produce cryogenic coolant temperatures; said cooling means being attached to the end of said dewar opposite said one end. 